In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder or powder suspension referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known and useful for light lens copying from an original and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly. In a slightly different arrangement, toner may be transferred to an intermediate surface, prior to retransfer to a final substrate.
Transfer of toner from the charge retentive surface to the final substrate is commonly accomplished electrostatically. A developed toner image is held on the charge retentive surface with electrostatic and mechanical forces. A substrate (such as a copy sheet) is brought into intimate contact with the surface, sandwiching the toner thereinbetween. An electrostatic transfer charging device, such as a corotron, applies a charge to the back side of the sheet, to attract the toner image to the sheet.
Unfortunately, the interface between the sheet and the charge retentive surface is not always optimal. Particularly with non-flat sheets, such as sheets that have already passed through a fixing operation such as heat and/or pressure fusing, or perforated sheets, or sheets that are brought into imperfect contact with the charge retentive surface, the contact between the sheet and the charge retentive surface may be non-uniform, characterized by gaps where contact has failed. There is a tendency for toner not to transfer across these gaps. A copy quality defect results.
That acoustic agitation or vibration of a surface can enhance toner release therefrom is known, as described by U.S. Pat. No. 4,111,546 to Maret, U.S. Pat. No. 4,684,242 to Schultz, U.S. Pat. No. 4,007,982 to Stange, U.S. Pat. No. 4,121,947 to Hemphill, Xerox Disclosure Journal "Floating Diaphragm Vacuum Shoe, by Hull et al., Vol. 2, No. 6, November/December 1977, U.S. Pat. No. 3,653,758 to Trimmer et al., U.S. Pat. No. 4,546,722 to Toda et al., U.S. Pat. No. 4,794,878 to Connors et al., U.S. Pat. No. 4,833,503 to Snelling, Japanese Published Patent Application 62-195685, U.S. Pat. No. 3,854,974 to Sato et al., and French patent No. 2,280,115.
Resonators for applying vibrational energy to some other member are known, for example in U.S. Pat. No. 4,363,992 to Holze, Jr., U.S. Pat. No. 3,113,225 to Kleesattel et al., U.S. Pat. No. 3,733,238 to Long et al., and U.S. Pat. No. 3,713,987 to Low.
Coupling of vibrational energy to a surface has been considered in Defensive Publication T893,001 by Fisler. U.S. Pat. No. 3,635,762 to Ott et al., U.S. Pat. No. 3,422,479 to Jeffee, U.S. Pat. No. 4,483,034 to Ensminger and U.S. Pat. No. 3,190,793 Starke.
Resonators coupled to the charge retentive surface of an electrophotographic device at various stations therein, for the purpose of enhancing the electrostatic function, are known, as in: U.S. Pat. No. 5,210,577 to Nowak; U.S. Pat. No. 5,030,999 to Lindblad et al.; U.S. Pat. No. 5,005,054, to Stokes et al.;; U.S. Pat. No. 5,010,369 to Nowak et al.; U.S. Pat. No. 5,025,291 to Nowak et al.; U.S. Pat. No. 5,016,055 to Pietrowski et al.; U.S. Pat. No. 5,081,500 to Snelling; U.S. patent application Ser. No. 08/003906 "Cross Process Vibrational Mode Suppression in High Frequency Vibratory Energy Producing Devices for Electrophotographic Imaging" by W. Nowak et al., and U.S. patent application Ser. No. 07/620,520, "Energy Transmitting Horn Bonded to an Ultrasonic Transducer for Improved Uniformity at the Horn Tip", by R. Stokes et al. Among the problems addressed in these references are uniformity of vibration, coupling of energy, optimal positioning within the transfer field, and the use in association with cleaning devices.
The utilization of a vacuum coupling arrangement is described in U.S. Pat. No. 4,987,456. A vacuum is applied by forming a vacuum chamber which surrounds the transducer with a photoconductive member p/r as an enclosing side of the chamber. This serves two main functions. One being to maintain the photoconductive member in intimate contact with the ultrasonic transducer with sufficient normal force such that coupling of the ultrasonic energy from the transducer into the photoconductive member can occur. Secondly, it is necessary to isolate the vibratory energy such that it vibrates the toner only in the xerographic transfer zone to prevent toner image disturbance. This is accomplished due to the normal force applied to the photoconductive member onto the surface of the vacuum chamber wall positioned upstream from the transducer in the process direction. While the vacuum coupling approach functions satisfactorily, the expense associated with the necessary hardware and vacuum pump are relatively high compared to the total cost associated with the Acoustic Transfer Assist hardware. In addition, the vacuum coupling creates additional machine noise, real estate, and potential reliability limitations. For these reasons, an alternative approach for coupling/damping is desirable.
All the references cited herein are specifically incorporated by reference for their teachings.